Mobile communications systems, such as cellular or personal communications services (PCS) systems, are made up of a plurality of cells. Each cell provides a radio communications center in which a mobile unit establishes a call with another mobile unit or a wireline unit connected to a public switched telephone network (PSTN). Each cell includes a radio base station, with each base station connected to a mobile switching center that controls processing of calls between or among mobile units or mobile units and PSTN units.
Several protocols exist for circuit-switched wireless communications, including the advanced mobile phone system (AMPS) standard, the TIA/EIA-136 time-division multiple access (TDMA) protocol from the Telecommunications Industry Association (TIA), the Global System for Mobile (GSM) TDMA protocol from the European Telecommunications Standards Institute (ETSI), and the IS-95, IS-95A, and IS-95B code-division multiple access (CDMA) standards from the TIA.
Traditional speech-oriented wireless systems utilize circuit-switched connection paths in which a line is occupied for the duration of the connection between a mobile unit and the mobile switching center. Such a connection is optimum for communications that networks (LANs), wide area networks (WANs), and the Internet use packet-switched connections, in which communication between nodes on a communications link is performed with data packets. Each node occupies the communications link only for as long as the node needs to send or receive data packets. Such communications are bursty in nature, with packets sent in bursts followed by periods of inactivity.
A wireless connection protocol that has been proposed to provide more efficient connections between a mobile unit and a packet-switched data network such as an Internet Protocol (IP) network is the General Packet Radio Service (GPRS) protocol, with versions complementing existing GSM systems and TIA/EIA-136 systems. In a GPRS communications system, various entities are present. A serving GPRS support node (SGSN) controls communications between mobile units and a packet-based data network. The SGSN is typically connected to a gateway GPRS support node (GGSN), which provides the interface to the packet-switched data network. The SGSN is connected to base station systems (BSS) over respective Gb interfaces, which provide for the exchange of control signaling and user data.
The Gb interface link layer may be based on the Frame Relay protocol, as described in TS 101 299, entitled “Digital Cellular Telecommunications System (Phase 2+); General Packet Radio Service (GPRS); Base Station System (BSS)—Serving GPRS Support Node (SGSN) Interface; Network Service,” GSM 08.16 Version 6.1.0, Release 1997 (hereinafter the “GSM 08.16 Standard”). In a Frame Relay network, permanent virtual connections (PVCs) are established between the SGSN and each base station system. A PVC is a predetermined logical path through the network between two points, in this case the SGSN and a base station system. Each PVC is associated with a data link connection identifier (DLCI), which is the identification of the PVC used by the network to find the right path and destination for a communicated frame of data. A further description of the Gb interface is provided in Draft ETSI EN 301 344, entitled “Digital Cellular Telecommunications System (Phase 2+); General Packet Radio Service (GPRS); Service Description; Stage 2,” GSM 03.60 Version 7.1.0, Release 1998 (hereinafter the “GSM 03.60 Standard”); and in ETSI TS 101 343, entitled “Digital Cellular Telecommunications System (Phase 2+); General Packet Radio Service (GPRS); Base Station (BSS)—Serving GPRS Support Node (SGSN); BSS GPRS Protocol (BSSGP),” GSM 08.18 version 7.0.0 Release 1998.
Communications according to the Frame Relay protocol are connection-oriented, and differ from communications over connectionless, packet-switched networks such as IP networks. The Frame Relay protocol is relatively tightly coupled to the underlying physical layer, such as a T1 or T3 layer. This limits the flexibility in how the Gb interface can be implemented.